The overall goal of this research is to identify the regulatory mechanisms operating in the control of protein synthesis, and to understand the molecular basis for this control. In this context, we are examining the role of the phosphorylation of S40 ribosomal subunits and other proteins involved in protein synthesis using the rabbit reticulocyte system. During the current year, the possible role of cyclic AMP-regulated phosphorylation of the S40 subunit in the regulation of protein synthesis will be examined. In addition attempts will be made to correlate the observed phosphorylation of two initiation factors by a cyclic nucleotide-independent protein kinase with the known functions of these factors in the initiation of protein synthesis. BIBLIOGRAPHIC REFERENCES: Traugh, J. A. and Porter, G. G., A comparison of ribosomal proteins from rabbit reticulocytes phosphorylated in situ and in vitro, Biochemistry 15, 610-616 (1976). Lightfoot, H. N., Mumby, M. and Traugh, J. A., Dephosphorylation of 40S ribosomal subunits by phosphoprotein phosphatase actvity from rabbit reticulocytes, Biochem. Biophys. Res. Commun. 66, 1141-1146 (1975).